[css-lists-3] Change counter inheritance to only take from prev sibling if the counter doesn't exist on the parent, per CSSWG resolution. w3c#5477

Author: tabatkins

css-lists-3/Overview.bs

@@ -1002,29 +1002,31 @@ Inheriting Counters</h4>
 		To <dfn>inherit counters</dfn>
 		into an |element|:
 
-		1. Let |element counters| be an initially empty [=CSS counters set=]
-			representing |element|’s own [=CSS counters set=].
+		1. If |element| is the [=tree/root=] of its document tree,
+			the element has an initially-empty [=CSS counters set=].
+			Return.
 
-		2. If |element| is the [=tree/root=] of its document tree,
-			return.
-			(The element has an initially-empty counter map
-			and inherits nothing.)
+		2. Let |element counters|,
+			representing |element|’s own [=CSS counters set=],
+			be a copy of the [=CSS counters set=]
+			of |element|'s parent element.
 
-		3. Let |counter source| be the [=CSS counters set=]
-			of |element|’s preceding sibling,
-			if it has one,
-			or else of |element|’s parent
-			if it does not.
+		3. Let |sibling counters| be the [=CSS counters set=]
+			of |element|'s preceding sibling (if it has one),
+			or an empty [=CSS counters set=] otherwise.
+
+			[=map/For each=] |counter| of |sibling counters|,
+			if |element counters| does not already contain a counter with the same [=name=],
+			append a copy of |counter| to |element counters|.
 
 		4. Let |value source| be the [=CSS counters set=]
 			of the element immediately preceding |element| in [=tree order=].
 
-		5. [=map/For each=] (|name|, |originating element|, |value|) of |value source|:
-			1. If |counter source| also [=set/contains=] a [=counter=]
-				with the same |name| and |originating element|,
-				then [=set/append=] a copy of |value source|’s [=counter=]
-				(|name|, |originating element|, |value|)
-				to |element counters|.
+			[=map/For each=] |source counter| of |value source|,
+			if |element counters| [=set/contains=] a [=counter=]
+			with the same [=name=] and [=creator=],
+			then set the the [=value=] of that counter
+			to |source counter|'s [=value=].
 	</div>
 
 	<div class='example' id='counter-inheritance-example'>